Method and system for locating a mobile terminal

ABSTRACT

A method and system locates a mobile terminal addressed in a location service request using an overlay identity. According to one aspect of the invention a location service client accesses a first subscriber database, thereby providing said overlay identity, in order to derive a cellular identity of said mobile terminal. According to another aspect of the invention the location service client accesses a location service server in order thereby providing said overlay identity. The location service server initiates a privacy check using said overlay identity and in response receives a cellular identity. The cellular identity then may be used to request a location service to enhance functionality.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.10/456,517, entitled “METHOD AND SYSTEM FOR LOCATING A MOBILE TERMINAL”,by T. Varonen, et al., filed Jun. 9, 2013, which is a Continuation InPart of application Ser. No. 10/384,628, entitled “METHOD AND SYSTEM FORLOCATING A MOBILE TERMINAL”, by T. Varonen, et al., filed Mar. 11, 2003,which claims the benefit of priority of Provisional Application No.60/439,442, entitled “METHOD AND SYSTEM FOR LOCATING A MOBILE TERMINAL”,by T. Varonen, et al., filed Jan. 13, 2003, the contents of each beingincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a method and system for locating amobile terminal in a cellular network based on a request received froman overlay system, such as a IP (Internet Protocol) Multimedia Subsystem(IMS).

BACKGROUND

In general, overlay systems may be provided in cellular or fixednetworks for enabling network operators to offer specific services basedon and built upon applications, services and protocols not supported intheir networks. The intention is that such services will be developed bythe network operators and other third party suppliers using themechanisms provided by external networks, such as the Internet or otherexternal network systems or subsystems.

Recently, an IP Multimedia core network Subsystem (IMS) has beendeveloped which comprises all core network elements for provision ofmultimedia services. This includes a collection of signalling and bearerrelated network elements as defined e.g. in the Third GenerationPartnership Project (3GPP) specification TS 23.002. IP Multimediaservices are based on an IETF (Internet Engineering Task Force) definedsession control capability which, along with multimedia bearers,utilizes the PS (Packet Switched) domain of the cellular network. Inorder to achieve access independence and to maintain a smooth operationwith wireless terminals across the Internet, the IMS attempts to beconformant to IETF “Internet Standards”. Therefore, the interfacesspecified conform as far as possible to these standards for the casewhere an IETF protocol has been selected, e.g. SIP (Session InitiationProtocol). The IMS enables the convergence of, and access to, voice,video, messaging, data and to web-based technologies for the wirelessuser, and combines the growth of the Internet with the growth in mobilecommunications.

As already mentioned, the IMS utilizes the PS domain to transportmultimedia signalling and bearer traffic. The PS domain maintains theservice while the mobile terminal moves and hides these moves from theIMS. The IMS is independent of the CS (Circuit Switch) domain althoughsome network elements may be common with the CS domain. This means thatit is not necessary to deploy a CS domain in order to support an IMSbased network. A mobile station (MS) consists of a mobile or userequipment (ME or UE) with a valid SIM (Subscriber Identity Module) orUSIM (Universal Mobile Telecommunications System Subscriber IdentityModule) attached. The abbreviation “UE” in this specification refersboth to MS and user equipment, even those used for emergency calls,which do not have a valid SIM or USIM.

A UE accessing an IMS service requires an IP address which is logicallypart of IMS IP addressing domain. There are various identities which maybe associated with a user of IP multimedia services. Every IMSsubscriber has one or more public user identities. The public useridentity is used by any user for requesting communications to otherusers. For example, this might be included on a business card. Bothtelecom numbering and Internet naming schemes can be used to addressusers depending on the public user identities allocated to the users.The public user identity may take the form of a SIP URL (UniformResource Locator) as defined in RFC 2543 and RFC 2396, or an E.164number. At least one public user identity is securely stored on the USIMand may be used to identify the user's information within a subscriberdatabase, e.g. the Home Subscriber Server (HSS), e.g. during mobileterminated set-up.

A location service (LCS) feature in UMTS and GSM (Global System forMobile Communications) provides a mechanism to support mobile locationservices for operators, subscribers and third party service providers.Location services may be considered as a network provided enablingtechnology consisting of standardized service capabilities which enablethe provision of location applications. The applications may be serviceprovider specific. In general, LCS is a service concept in a systemstandardization. LCS specifies all necessary network elements andentities, their functionalities, interfaces as well as communicationmessages to implement the positioning functionality in a cellularnetwork. Positioning is a functionality which detects a geographicallocation of e.g. a mobile terminal. Principles and/or algorithms onwhich the estimation of the geographical location is based may be e.g.AOA, TOA or TDOA. For example, the Global Positioning System (GPS) isbased on TOA while OTDOA and E-OTD (on GSM) are based on TDOA.

The positioning of the UE is a service provided by the access network.In particular, all access networks (e.g. UMTS Terrestrial Radio AccessNetwork (UTRAN), GM/EDGE (Enhanced Datarate for GSM Evolution) RadioAccess Network (GERAN), which facilitate determination of the locationsof UEs, shall be able to exchange location information with a corenetwork as defined in the 3GPP specification TS23.271, when connected toa core network.

By making use of the radio signals, the capability to determine the(geographic) location of the UE can be provided. The locationinformation may be requested by and reported to a client (application)associated UE or by a client within or attached to the core network. Thelocation information may also be utilized internally in a system, forexample, for location assisted handover or to support other features,such as home location billing. The position information may be reportedin standard, e.g. geographical coordinates, together with thetime-of-day and the estimated errors (uncertainty) of the location ofthe UE according to the 3GPP specification TS 23.032. There are manydifferent possible uses for the location information. As alreadymentioned, the positioning feature may be used internally by theGSM/UMTS network (or attached networks), by value-added networkservices, by the UE itself or through the network and by the thirdparties' services. The positioning feature may also be used by anemergency service. Although LCS has been defined for the CS and PSdomains of cellular networks, it has not yet been defined for the IMSdomain. Currently, the LCS service does not support IMS LCS clients tobe addressed by IMS identities.

BRIEF SUMMARY

It is therefore an object of the present invention to provide a methodand system for locating a mobile terminal addressed by an overlayidentity used in an overlay system, e.g. an IMS identity used in theIMS.

According to a first aspect of a preferred embodiment of the inventionthis object is achieved by a method of locating a mobile terminal in acellular network, said method comprising a) a location service client(80) accessing a first subscriber database, thereby providing an overlayidentity, b) said first subscriber database in response returning acellular identity of said mobile terminal (10), c) said location serviceclient (80) using said cellular identity to request a location servicefrom a location service server d) said location service server usingsaid cellular identity to access the first or a second subscriberdatabase e) said first or second subscriber database in responsereturning a routing information of said mobile terminal (10), and f)said location service server initiating a location service of saidcellular network based on said cellular identity and on said derivedrouting information.

According to a second aspect which constitutes a further development ofthe first aspect of a preferred embodiment of the invention, thelocation service client is an IMS server and the overlay identity is anIMS identity.

According to a third aspect which constitutes a further development ofthe first or second aspect of a preferred embodiment of the invention,the first subscriber database is a Home Subscriber Server.

According to a fourth aspect which constitutes a further development ofthe second or third aspect of a preferred embodiment of the invention,said IMS server is a SIP application server and said IMS identity is aSIP URL.

According to a fifth aspect which constitutes a further development ofthe fourth aspect of a preferred embodiment of the invention, in step a)said SIP application server accesses said Home Subscriber Serverutilizing a Sh interface.

According to a sixth aspect which constitutes a further development ofanyone of the first to fifth aspects of a preferred embodiment of theinvention, said location service server is a Gateway Mobile LocationCenter.

According to a seventh aspect which constitutes a further development ofanyone of the first to sixth aspects of a preferred embodiment of theinvention, said step f) is performed by using aMAP-SEND-ROUTING-INFO-FOR-LCS service function.

According to an eighth aspect which constitutes a further development ofanyone of the first to seventh aspects of a preferred embodiment of theinvention, said cellular identity is an MSISDN or IMSI.

According to a ninth aspect which constitutes a further development ofanyone of the first to eighth aspects of a preferred embodiment of theinvention, said routing information is an address of a network element,having a switching function in said cellular network.

Additionally, according to tenth aspect of a preferred embodiment of theinvention the above object is achieved by a system for locating a mobileterminal in a cellular network, said system comprising: a locationservice client having an overlay identity of said mobile terminal, afirst subscriber database storing a cellular identity of said mobileterminal, which first subscriber database is arranged to be accessibleby said location service client and to derive a cellular identity ofsaid mobile terminal based on the overlay identity provided by saidlocation service client, a location service server arranged to receive alocation request of said location service client including said cellularidentity of said mobile terminal, which location service server isarranged to use said cellular identity for an access to the firstsubscriber database or a second subscriber database in order to derive arouting information, and to initiate a location service of said cellularnetwork based on said routing information and said cellular identity.

According to a eleventh aspect which constitutes a further developmentthe tenth aspect of a preferred embodiment of the invention, the firstsubscriber database is a Home Subscriber Server.

According to a twelfth aspect which constitutes a further development ofthe tenth or eleventh aspect of a preferred embodiment of the invention,the location service client is part of an IMS and said overlay identityis an IMS identity.

According to a thirteenth aspect which constitutes a further developmentof the twelfth aspect of a preferred embodiment of the invention, saidlocation service client is a SIP application server and said IMSidentity is a SIP URL.

According to a fourteenth aspect which constitutes a further developmentof the thirteenth aspect of a preferred embodiment of the invention,said first subscriber database comprises a HLR multimedia functionalitypart and an IP multimedia functionality part.

According to a fifteenth aspect which constitutes a further developmentof the fourteenth aspect of a preferred embodiment of the invention,said cellular identity is stored in the IP multimedia functionality partof said first subscriber database.

According to a sixteenth aspect which constitutes a further developmentof the fourteenth aspect of a preferred embodiment of the invention, aninternal interface is arranged within said first subscriber database forutilizing pointers between both functionality parts.

According to a seventeenth aspect which constitutes a furtherdevelopment of the fourteenth aspect of a preferred embodiment of theinvention, said location service server is a Gateway Mobile LocationCenter (50).

According to an eighteenth aspect which constitutes a furtherdevelopment of anyone of the tenth to seventeenth aspects of a preferredembodiment of the invention, said second subscriber database is a HomeSubscriber Server or a Home Location Register of said cellular network.

Additionally, according to a nineteenth aspect of a preferred embodimentof the invention the above object is achieved by a method of locating amobile terminal in a cellular network, said method comprising: a) alocation service client accessing a location service server in order torequest a location service thereby providing an overlay identity; b)said location service server sending a conversion request to a PrivacyProfile using said overlay identity; c) in response to said conversionrequest a cellular identity being returned; d) said location serviceserver using said cellular identity to access a subscriber database; e)said subscriber database in response returning a routing information ofsaid mobile terminal; and f) said location service server initiating alocation service of said cellular network based on said cellularidentity and on said derived routing information.

According to a twentieth aspect which constitutes a further developmentof the nineteenth aspect of a preferred embodiment of the invention saidconversion request is sent in the context of a privacy check; and saidcellular identity is returned in response to said privacy check.

According to a twenty first aspect which constitutes a furtherdevelopment of anyone of the nineteenth or twentieth aspects of apreferred embodiment of the invention said location service servercontains privacy profile register functionality including a relationbetween the overlay identity and the cellular identity;

According to a twenty second aspect which constitutes a furtherdevelopment of anyone of the nineteenth or twentieth aspects of apreferred embodiment of the invention said privacy check is performed byaccessing a privacy profile register containing a relation between saidoverlay identity and said cellular identity;

According to a twenty third aspect which constitutes a furtherdevelopment of anyone of the nineteenth to twenty second aspects of apreferred embodiment of the invention said location service client is anIMS server and said overlay identity is an IMS identity.

According to a twenty fourth aspect which constitutes a furtherdevelopment of the twenty third aspect of a preferred embodiment of theinvention said IMS server is a SIP application server and said IMSidentity is a SIP URL.

According to a twenty fifth aspect which constitutes a furtherdevelopment of anyone of the nineteenth to twenty fourth aspects of apreferred embodiment of the invention said location service server is aGateway Mobile Location Center.

According to a twenty sixth aspect which constitutes a furtherdevelopment of anyone of the nineteenth to twenty fifth aspects of apreferred embodiment of the invention said step d) is performed by usinga MAP-SEND-ROUTING-INFO-FOR-LCS service function.

According to a twenty seventh aspect which constitutes a furtherdevelopment of anyone of the nineteenth to twenty sixth aspects of apreferred embodiment of the invention said cellular identity is anMSISDN or IMSI.

According to a twenty eighth aspect which constitutes a furtherdevelopment of anyone of the nineteenth to twenty seventh aspects of apreferred embodiment of the invention said routing information is anaddress of a network element, having a switching function in saidcellular network.

Additionally, according to a twenty ninth aspect of a preferredembodiment of the invention the above object is achieved by system forlocating a mobile terminal in a cellular network, said system comprisinga subscriber database, a location service client having an overlayidentity of said mobile terminal, and a location service server arrangedto receive a location request from said location service clientincluding said overlay identity, said location service server furtherbeing arranged to use said overlay identity for sending a conversionrequest to a Privacy Profile, to receive a cellular identity in responseto said conversion request, to use said cellular identity for an accessto said subscriber database in order to derive a routing information,and to initiate a location service of said cellular network based onsaid routing information and said cellular identity.

According to a thirtieth aspect which constitutes a further developmentof the twenty ninth aspect of a preferred embodiment of the inventionsaid location service server is arranged to send said conversion requestin the context of a privacy check; and to receive said cellular identityin response to said privacy check.

According to a thirty first aspect which constitutes a furtherdevelopment of anyone of the twenty ninth or thirtieth aspects of apreferred embodiment of the invention said location service servercontains privacy profile register functionality including a relationbetween the overlay identity and the cellular identity;

According to a thirtieth second aspect which constitutes a furtherdevelopment of the twenty ninth or thirtieth aspects of a preferredembodiment of the invention said system further comprises a privacyprofile register containing a relation between said overlay identity andsaid cellular identity and being accessible by said location serviceserver;

According to a thirty third aspect which constitutes a furtherdevelopment of anyone of the twenty ninth to thirtieth second aspects ofa preferred embodiment of the invention said location service client ispart of an IMS and said overlay identity is an IMS identity.

According to a thirty fourth aspect which constitutes a furtherdevelopment of the thirty third aspect of a preferred embodiment of theinvention said location service client is a SIP application server andsaid IMS identity is a SIP URL.

According to a thirty fifth aspect which constitutes a furtherdevelopment of anyone of the twenty ninth to thirty fourth aspects of apreferred embodiment of the invention said location service server is aGateway Mobile Location Center.

According to a thirty sixth aspect which constitutes a furtherdevelopment of the thirty fifth aspects of a preferred embodiment of theinvention said Gateway Mobile Location Center contains domain addressinformation corresponding to the mobile terminal Home Gateway MobileLocation Center.

According to a thirty seventh aspect which constitutes a furtherdevelopment of the thirty fifth aspects of a preferred embodiment of theinvention said system further comprises a database containing domainaddress information, whereby said Gateway Mobile Location Center isfurther arranged to send a query to said database in order to derivedomain address information corresponding to the mobile terminal HomeGateway Mobile Location Center.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the present invention will be described in greaterdetail based on a preferred embodiment with reference to theaccompanying drawings, in which:

FIG. 1 shows a network architecture for implementing a location servicefunction according to a preferred embodiment of the present invention;

FIG. 2 shows a signaling diagram indicating exchanged signaling messagesand procedures in a location service function according to the preferredembodiment of the present invention shown in FIG. 1;

FIG. 3 shows an example of a generic HSS structure and some basisinterfaces;

FIG. 4 shows a network architecture for implementing a location servicefunction according to another preferred embodiment of the presentinvention; and

FIG. 5 shows a signaling diagram indicating exchanged signaling messagesand procedures in a location service function according to the preferredembodiment shown in FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A preferred embodiment will now be described based on an LCSarchitecture in a UMTS network as shown in FIG. 1. According to FIG. 1,a reference point, called Le Interface, is shown between an LCS server(here: GMLC 50) and an LCS client 80 which, in the present embodiment,is an IMS application server or application. The Le reference point isdescribed in the 3GPP Specification TS 23.271. However, there may bemore than a single LCS network interface to several different LCSclients or other networks. These networks may both differ in ownershipas well as in communications protocol. The network operator may defineand negotiate inter-connection with each external LCS client or othernetwork. In general, an interface differs from a reference point in thatan interface is defined where specific LCS information is exchanged andneeds to be fully recognized.

Furthermore, an interface called Lg is arranged to connect the LCSserver (here GMLC) and a core network (2G-MSC, 2G-/3G-SGSN, MSC server)in order to request location information or, more general, to connecttwo independent LCS networks, e.g. different PLMNs (Public Land MobileNetworks) for message exchange. The LCS functional entities are groupedinto an LCS client functional group and an LCS server functional group.The LCS server functional group consists of functions in the UMTS PLMNsupporting LCS, e.g. a client handling component, a system handlingcomponent, a subscriber handling component, and a positioning component.The LCS client 80 contains a LCS component with one or more clients,which by using location information can provide location based services.In particular, the LCS client 80 is a logical functional entity thatrequests from the LCS server in the PLMN location information for one ormore than one target UE, i.e. a UE 10 shown in FIG. 1, within aspecified set of parameters such as Quality of Service of QoS.

In the present architecture shown in FIG. 1, the LCS client 80 residesin an external entity belonging to an overlay system, i.e. the IMS. Viaa location service request, the LCS client 80 communicates with the LCSserver, i.e. GMLC 50, to request for the location information of the UE10. Attributes identified by the location service request may be targetUE, LCS identity, state, event, requested QoS information, localcoordinate reference system, and/or geographical area. A locationservice response is sent to the LCS client 80 as the result of thelocation service request issued by the LCS server. Attributes identifiedfor the location service response may be the location indication of theUE 10 in geographical coordinates, the location of the UE 10 as anellipsoid with axes and direction of all axes, an estimated achievedQoS, and/or an indication when UE 10 enters or leaves the geographicalarea.

FIG. 1 illustrates generally the relation of the LCS client 80 andservers in the core network with a GERAN 20 and a UTRAN 30. The LCSentities within the access networks communicate with the core networkconsisting of a 2G-MSC 22 of the CS domain, a 2G-SGSN 24 of the PSdomain, a 3G-SGSN 32 of the PS domain, and an MSC server 34 of the CSdomain across A, Gb and Iu interfaces. Communication among the accessnetwork LCS entities makes use of the messaging and signalingcapabilities of the access network.

Furthermore, a subscriber database, i.e. a HLR/HSS 40 is provided forstoring subscriber specific data of the UE 10 and other mobile terminalsor equipments. It is noted that the HLR and HSS may be arranged atdifferent locations, while the HLR part may include both 2G-HLR and3G-HLR functionalities. In this respect it is noted, that the terms “2G”and “3G” denote second and third generation mobile communicationfunctionalities, respectively.

With this configuration both the network and the UE 10 are able tomeasure the timing of signals and compute a location estimate of the UE10. Depending on the applied positioning method it is possible toutilize the corresponding configuration containing all needed entities.For instance, if network-based positioning is applied, the entities thatare involved in measuring the mobile's signal and calculating itslocation estimate are allocated to the network elements of the accessstratum. On the other hand, in case mobile-based or network-assistedmethods are used entities should be allocated to the UE 10.

The GMLC 50 contains functionality required to support LCS. In one PLMN,there may be more than one GMLC. The GMLC 50 is the first node theexternal LCS client 80 accesses in a GSM PLMN (i.e. the Le referencepoint is supported by the GMLC 50). The GMLC 50 may request routinginformation from the HLR/HSS 40 via a Lh interface. After performingregistration authorization, it sends positioning requests to either the2G-MSC 22, SGSNs 24, 32 or MSC server 34 and receives final locationestimates from the corresponding entity via the Lg interface. It isnoted that several GMLCs may be involved, e.g. a source or requestingGMLC (R-GMLC) accessible directly by the external client, a home GMLC(H-GMLC) of the targeted UE and, where required, a visited GMLC (V-GMLC)connected with the core network the targeted UE presently roams. In thiscase the information flow between the GMLCs may for example beestablished via a standardized Lr interfaces, as proposed by 3GPP TS23.271, see also FIG. 4.

The UE 10 may be involved in various positioning procedures. Specific UEinvolvement is specified in each of the positioning procedures mentionedin the 3GPP specification TS 25305 for the UTRAN 30 and TS 43.059 forthe GERAN 20. The 2G-MSC 22 contains a functionality responsible for UEsubscription authorization and managing call related and non-callrelated positioning requests of LCS. The 2G-MSC 22 is accessible to theGMLC 50 via the Lg interface. The LCS functions of the 2G-MSC 22 arerelated to charging and billing LCS coordination, location requestauthorization and operation of the LCS services. If connected to the2G-SGSN 24 through a Gs interface, it checks whether the UE 10 is GPRSattached to decide whether to page the UE 10 on the A or Gs interface.

The MSC server 34 handles the same functionality as the 2G-MSC 22including charging and billing, LCS coordination, location requests,authorization and operation of the LCS services. The MSC server 34 isaccessible to the GMLC 50 via the Lg interface. Furthermore, the 2G- and3G-SGSNs 24, 32 contain a functionality responsible for UE subscriptionauthorization and managing positioning requests of LCS. The SGSNs 24, 32are accessible to the GMLC via the Lg interface. The LCS functions ofthe SGSNs 24, 32 are related to charging and billing, LCs coordination,location request, authorization and operation of the LCS services. TheSGSNs 24, 32 forward the CS paging request received from the Gsinterface to a base station subsystem or radio network controller of therespective access network.

The HLR/HSS 40 is accessible from the GMLC 50 via a Lh interface. For aroaming UE, the HLR/HSS 40 may be in a different PLMN.

Furthermore, a gsmSCF (GSM service control function) provides an Lcinterface to support access between the LCS and a network functionalityCAMEL (Customized Applications for Mobile Network Enhanced Logic)providing the mechanisms of Intelligent Network to a mobile user. Theprocedures and signaling associated with it are defined in the 3GPPspecification TS 23.078 and TS 29.002, respectively.

An important point is the possibility to address and indicate the targetUE 10 using a cellular identity, e.g. the MSISDN (Mobile StationIntegrated Services Data Network) or IMSI (International MobileSubscriber Identity), or the like. However, in the present case, theexternal LCS client 80 belongs to the IMS and thus uses an IMS identityin the location service request supplied to the GLMC 50. Therefore, amapping function is provided for mapping the IMS identity of the UE 10with a routing information required for accessing the HLR/HSS 40allocated to the target UE 10. Thereby, an IP addressing of the targetUE 10 can be performed without requiring an active PDP contextestablished between the target UE 10 and the external LCS client 80.

The Lh interface between the GMLC 50 and the HLR/HSS 40 may be based ona Mobile Application Part (MAP) protocol. This interface Lh is used bythe GMLC 50 to request a routing information to the serving MSC or SGSNof the particular target UE 10 whose location has been requested. The Lginterface is used by the GMLC 50 to convey the location request to therespective MSC or SGSN function currently serving the target UE 10.Furthermore, the Lg interface is used by the respective MSC or SGSNfunction to return location results to the GMLC 50.

For the LCS service, a MAP-SEND-ROUTING-INFO-FOR-LCS service is usedbetween the GMLC 50 and the HLR/HSS 40 to retrieve the routinginformation needed for routing a location service request to the servingMSC or SGSN function.

However, the LCS client has only an overlay or IMS identity of thetarget UE 10. The LCS client sends a conversion request directly to theHSS (see lower dashed line in FIG. 1) in order to retrieve a targetsubscriber identity, such as IMSI or MSISDN. The HSS returns the targetsubscriber identity to the LCS client. If the LCS client is understoodas an application server of an IMS then a Sh reference point could beutilized to exchange information between the LCS client and the HSS. Forexample Sh-pull and Sh-pull resp procedures such as specified in 3GPP TS29.328 could be utilized to obtain the subscriber identity of the targetUE 10 from the HSS. In particular, the subscriber database access may beperformed by sending a Sh-pull message containing at least an useridentity information element, e.g. a user public identity such asSIP-URL, and a requested data information element, e.g. aPublicIdentifiers XML tag and others, indicating the list of referencesto the requested information. The requested information in this case atleast comprise a List of public identities. In response the HSS sends aSh-pull resp message which contains said List of public identities ofthe user in the requested data information element (PublicIdentifiers).Note; that the PublicIdentifiers element according to the presentspecification 3GPP TS 29.328 contains SIP URL, TEL URL, and MSISDNidentities which may be returned to the LCS client. However, the contentmay be extended to IMSI identity, too. Alternatively a new class underSh data may be created and corresponding access key may be defined.

Just as well a new interface may be implemented between the LCS clientand HSS.

Using the target subscriber identity the LCS client 80 invokes the GMLC50 via the Le interface in order to accesses the HLR/HSS 40 by a MAPquery via the Lh interface, e.g. a MAP-SEND-ROUTING-INFO-FOR-LCSmessage. Using the cellular identity, the GMLC 50 initiates via the Lginterface a location service function within the cellular networkidentified by the routing information (address of the serving networkelement) obtained by the MAP query. Thereby, an IMS LCS servicefunctionality can be provided in the UMTS/GSM network architecture.

FIG. 2 shows a signaling diagram indicating basic signaling messages andprocedures required for the location service function. In particular, instep 1 the external LCS client 80 directly accesses HSS 40 requestingfor conversion of the IMS identity to the cellular identity (IMSI orMSISDN). After receiving the subscriber identity (step 2) the LCS client80, accordingly, may send in step 3 a location service request to theGMLC 50 containing the identity target subscriber information. Then instep 4, a MAP-SEND-ROUTING-INFO-FOR-LCS service may be invoked by theGMLC 50 based on the received subscriber identity in order to retrievethe second routing information from the HLR/HSS 40. After receiving therouting information to the serving network element (step 5) the locationservice procedure can be invoked by GMLC 50 in the cellular network(step 6). Finally in step 7, the GMLC 50 sends the location serviceresponse received from the cellular network to the external LCS client80.

According to an example of a generic HSS logical structure as specifiedin 3GPP TS 23.002, see FIG. 3, the HSS is the master database for agiven user. It is the entity containing the subscription-relatedinformation to support the network entities actually handlingcalls/sessions. The HSS is responsible for holding user relatedinformation such as: user identification (cellular identity), numberingand addressing information; user security information (not shown); userlocation information at internet-system level (not shown); and userprofile information (not shown). The HSS may integrate heterogeneousinformation, and enable enhanced features in the core network to beoffered to the application & services domain. According to presentstandards (3GPP TS 23.002), the HSS consists of IP multimediafunctionality to provide support to control functions of IM subsystemssuch as the CSCF. IP multimedia functionality is needed to enablesubscriber usage of the IM CN subsystem services. This IP multimediafunctionality is independent of the access network used to access the IMCN subsystem. HSS further consists of the subset of the HLR/AUCfunctionality required by the PS domain of The subset of HLR/AUCfunctionality required by the CS domain.

As can be seen from FIG. 3, according to the present standard, the LCSclient, if is understood as an application server of an IMS,communicates with the HSS via the Sh reference point. By this means aconversion request may be sent directly to the HSS in order to retrievea target subscriber identity.

However, there is yet no standardized interface between the abovefunctionalities within the HSS. Therefore, IP multimedia functionalityis not aware of identities which belong to HLR and vice versa. Further,when using Cx or Sh interfaces e.g. IMSI can not be retrieved and on theother hand, when using Gc, Gr, C, D, Lh e.g. IMS identities can not beretrieved.

In order to enable the HSS to return target subscriber identities(cellular identity) to the LCS client when IP multimedia functionalityis addressed by the provided IMS identity (SIP URL), target subscriberidentities either may be stored in the IP multimedia functionality partof HSS, an internal interface is to be arranged utilizing pointersbetween both functionality parts, or an internal interface between HLRand IP multimedia functionality is to be established.

The main difference between the first preferred embodiment as describedin conjunction with FIGS. 1 through 3 and the second preferredembodiment is that in the latter the LCS client does not directly accessthe subscriber database 40. In order to request for a LCS service theclient contacts the location service server, e.g. a GMLC. Since only anoverlay identity, such as a SIP URL, is available either a privacy checkusing said overlay identity may be executed by the location serviceserver, whereby a conversion request is sent in the context of theprivacy check. In response to the privacy check, more precisely to theconversion request, a cellular identity is returned. Or alternatively,the GMLC may send a separate conversion request with the overlayidentity to a subscribers Privacy Profile in response to which thecellular identity then will be returned. The latter solution might alsobe useful in cases where a privacy check is not needed. In both cases,the privacy profile which contains the requested privacy information ofa user further has to comprise a relation between the overlay identity(IMS) and the cellular (IMSI/MSISDN) identity. Such a privacy check orseparate request may either be executed accessing a privacy profileregister 60 (PPR), whereby, the PPR 60 is a standalone network entity,see network architecture shown in FIG. 4. Or the PPR functionality maybe integrated in H-GMLC, i.e. the H-GMLC itself contains the privacyprofile. The PPR 60 is standardized in 3GPP specification 23.271. TheHLR or HSS 40 contains the address to the PPR 60 or the H-GMLC mayalready have the PPR address e.g. from internal lookup table. The PPR 60is accessible from the H-GMLC via the Lpp interface.

The target UE's privacy profile settings shall always be checked in theUE's home PLMN prior to delivering a location estimate. However, in FIG.4 a situation is shown where the requesting GMLC 52 (R-GMLC), which isthe GMLC receiving the request from LCS client, is not the H-GMLC 54,which is responsible to control the privacy checking of the targetmobile. In order to allow location request from a GMLC outside the homePLMN while having privacy check in the home PLMN, the Lr interface isneeded. The problem that arises in such a situation is that beforemaking a privacy check the cellular identity is still unknown. On theother hand, the R-GMLC does not have the subscriber privacy profile.Hence, it cannot resolve the related cellular identity. Therefore,R-GMLC should either have a routing table containing domain addressescorresponding to a certain H-GMLC address or a query should be sent toan external database such as a DNS 90 (domain name server, not shown inFIG. 4) lookup query containing domain addresses. Since from the IMSidentity it is possible to find out the domain address and since theGMLC address is a URI as e.g. specified in RFC2396 the R-GMLC will thenbe able to forward the request to the corresponding H-GMLC.

Using the target subscriber identity, as before, the GMLC 50 (accordingto FIG. 4, the H-GMLC 54) via the Le interface accesses the HLR/HSS 40by a MAP query via the Lh interface, e.g. aMAP-SEND-ROUTING-INFO-FOR-LCS message. As illustrated in FIG. 4, whenthe UE is roaming a visited GMLC 56 (V-GMLC), which is the GMLC beingassociated with the serving node of the target mobile, using thecellular identity initiates via the Lg interface a location servicefunction within the cellular network identified by the routinginformation (address of the serving network element) obtained by the MAPquery. Thereby, an IMS LCS service functionality can be provided in theUMTS/GSM network architecture. Of course the second preferred embodimentis not restricted to a situation as shown in FIG. 4. It may apply in asituation where the requesting GMLC 52 is the visited GMLC 56, which maybe the home GMLC 54 in the same time. Any other constellation ispossible, too.

As illustrated in FIG. 5 the external LCS client 80 requests the currentlocation of a target UE 10 from a GMLC, in particular from R-GMLC 52,thereby providing an overlay identity such as IMS identity only (step1). The R-GMLC in this case performs a (standardized) DNS lookup queryfrom DNS server 90 (step 2) in order to derive the location of theH-GMLC 54 of the target UE 10 (step 3). However, this information may aswell be retrieved by a query procedure not yet standardized or bysearching an internal routing table belonging to each R-GMLC 52, forexample. If the R-GMLC 52 is the H-GMLC 54 of the target UE 10, i.e. theR-GMLC 52 stores the UE's privacy profile, then steps 4 and 9 areskipped. Otherwise, the R-GMLC 52 sends the location request to theH-GMLC 54 (step 4). In the next step the H-GMLC 54 verifies LCS barringrestrictions in the privacy profile of the targeted user contained inthe H-GMLC 54 or in PPR 60, as shown in FIG. 5. I.e., the H-GMLC 54sends the LCS authorisation request to the PPR 60, which request carriesthe type of location information requested (e.g. current location), theUE subscriber's IMS (or any other overlay) identity (not beingconcordant with the present 3GPP standard TS 23.271). PPR performs theprivacy check based on the target UE's privacy profile. The result ofthat privacy check and the cellular identity (IMSI/MSISDN) which,according to this preferred embodiment, is stored together with theprivacy profile information is send to GMLC in the LCS Authorisationresponse. If the location service request is to be barred and the LCSclient 80 does not have the override capability, an error response isreturned to the R-GMLC 52 or the LCS client 80.

According to an alternative solution, the H-GMLC may send a separaterequest (not shown in FIG. 5) to PPR in order to derive the cellularidentity.

As a next step 7 the normal routing (MAP-Send-routing-for-LCS-Inforequest, if the UE is roaming in V-GMLC) and LCS procedure takes placeas described above and specified in the standards. As a result theH-GMLC receives a location service response. In case an additionalprivacy check was requested to be performed after the positioningprocedure the LCS Authorisation Request shall also include the locationestimate.

If the privacy check in step 5 indicates that further privacy checks areneeded, or on the basis of the privacy profile, the H-GMLC optionallymay perform an additional privacy check (step 8). The H-GMLC 54 sendsthe location service response to the R-GMLC 52 (step 9). Finally, theR-GMLC 52 sends the location service response to the LCS client 80 (step10).

It is to be noted that the preferred embodiments of the presentinvention are not restricted to the provision of a location service in aIMS environment, but can be used for providing a location service in anyoverlay system having an own overlay identity allocated to the targetmobile terminal. Thus, the preferred embodiment may vary within thescope of the attached claims.

The invention claimed is:
 1. A method comprising: receiving, at agateway mobile location center, a request to locate a mobile terminal ina cellular network from a location service client, wherein the requestincludes, at least in part, an overlay identity that staticallyidentifies the mobile terminal to an overlay network without an activecontext established with the mobile terminal; causing, at least in part,a transmission of a query from the gateway mobile location center to adatabase, wherein the query includes, at least in part, a request fordomain address information corresponding to a mobile terminal homegateway mobile location center; causing, at least in part, a receptionof the requested domain address information at the gateway mobilelocation center from the database; causing, at least in part, from thegateway mobile location center a transmission of a conversion request tothe mobile terminal home gateway location center for a determination ofa cellular identity of the mobile terminal via a Privacy ProfileRegister based, at least in part, on the overlay identity; initiating anaccess of a subscriber database using the cellular identity to determinerouting information for the mobile terminal; and initiating a locationservice of the cellular network based on the cellular identity and therouting information to provide a geographical location of the mobileterminal.
 2. A method of claim 1, wherein the transmission of the of theconversion request is based, at least in part, on the domain addressinformation.
 3. A method of claim 1, wherein the transmission of theconversion request is in a context of a privacy check, and wherein thecellular identity is returned in response to the privacy check.
 4. Amethod of claim 1, wherein the location service client is an internetprotocol multimedia system (IMS) server and the overlay identity is anIMS identity.
 5. A method of claim 4, wherein the IMS server is asession initiation protocol (SIP) application server and the IMSidentity is a SIP uniform resource locator (URL).
 6. A method of claim1, wherein the location service is performed by using aMAP-SEND-ROUTING-INFOFOR-LCS service function.
 7. A method of claim 1,wherein the cellular identity is a mobile station integrated servicesdata network (MSISDN) identity or an international mobile subscriberidentity (IMSI).
 8. A method of claim 1, wherein the routing informationis an address of a network element, having a switching function in thecellular network.
 9. An apparatus comprising: at least one processor;and at least one memory including computer program code for one or moreprograms, the at least one memory and the computer program codeconfigured to, with the at least one processor, cause the apparatus toperform at least the following, receive, at a gateway mobile locationcenter, a request to locate a mobile terminal in a cellular network froma location service client, wherein the request includes, at least inpart, an overlay identity that statically identifies the mobile terminalto an overlay network without an active context established with themobile terminal; cause, at least in part, a transmission of a query fromthe gateway mobile location center to a database, wherein the queryincludes, at least in part, a request for domain address informationcorresponding to a mobile terminal home gateway mobile location center;cause, at least in part, a reception of the requested domain addressinformation at the gateway mobile location center from the database;cause, at least in part, from the gateway mobile location center atransmission of a conversion request to the mobile terminal home gatewaylocation center for a determination of a cellular identity of the mobileterminal via a Privacy Profile Register based, at least in part, on theoverlay identity; initiate an access of a subscriber database using thecellular identity to determine routing information for the mobileterminal; and initiate a location service of the cellular network basedon the cellular identity and the routing information to provide ageographical location of the mobile terminal.
 10. An apparatus of claim9, wherein the transmission of the of the conversion request is based,at least in part, on the domain address information.
 11. An apparatus ofclaim 9, wherein the transmission of the conversion request is in acontext of a privacy check, and wherein the cellular identity isreturned in response to the privacy check.
 12. An apparatus of claim 9,wherein the location service client is an internet protocol multimediasystem (IMS) server and the overlay identity is an IMS identity.
 13. Anapparatus of claim 12, wherein the IMS server is a session initiationprotocol (SIP) application server and the IMS identity is a SIP uniformresource locator (URL).
 14. An apparatus of claim 9, wherein thelocation service is performed by using a MAP-SEND-ROUTING-INFOFOR-LCSservice function.
 15. An apparatus of claim 9, wherein the cellularidentity is a mobile station integrated services data network (MSISDN)identity or an international mobile subscriber identity (IMSI).
 16. Anapparatus of claim 9, wherein the routing information is an address of anetwork element, having a switching function in the cellular network.